丙烯酸-丙烯酰胺共聚物吸水树脂的制备

采用溶液聚合法,以丙烯酸(AA)和丙烯酰胺(AM)为单体,N,N’-亚甲双丙烯酰胺(NMBA)为交联剂,过硫酸铵为引发剂,制备了丙烯酸-丙烯酰胺共聚物吸水树脂,探讨了单体配比(mAA/mAM)、交联剂和引发剂用量对树脂吸水率的影响。结果表明:在65℃时,丙烯酸-丙烯酰胺共聚物吸水树脂的最佳制备条件为:丙烯酸和丙烯酰胺质量比为4:1,交联剂和引发剂用量分别为聚合单体(丙烯酸和丙烯酰胺)总质量的0.02%和0.4%。     

不同引发体系对丙烯酰胺/丙烯酸盐共聚物溶液性能的影响

用五种不同类型的引发剂,采用水溶液聚合法制备了超高分子量聚丙烯酰胺/丙烯酸盐共聚产品。固定丙烯酰胺和丙烯酸盐单体配比、丙烯酰胺和丙烯酸盐浓度,改变引发剂种类和用量,考查了不同种类引发剂和用量对丙烯酰胺/丙烯酸盐共聚物分子量以及不同种类引发剂对粘弹性的影响,从而得到一组配伍性能较好的引发剂,使丙烯酰胺/丙烯酸盐共聚物分子量达到2.1×10~7。     

含丙烯酸的二元无规共聚物的抗硬水性能研究

本文通过将聚丙烯酰胺水解的方式合成了类似于无规共聚丙烯酰胺-丙烯酸的部分水解聚丙烯酰胺,并合成了无规共聚N-异丙基丙烯酰胺-丙烯酸(P(NIPAM-co-AA))。采用透射电子显微镜观察了两种二元共聚物在水溶液中聚集体的形貌。为了考察含丙烯酸的二元共聚物的抗硬水性能,测定了其钙皂分散力及钙离子稳定性,并与聚丙烯酸(PAA)比较。实验表明,P(NIPAM-co-AA)在水中形成稳定的囊泡状聚集体,并具有更强的钙皂分散力。     

原油降凝剂CAA的合成及降凝效果的研究

本文报导了原油降凝剂丙烯酸烷基酯-丙烯酰胺共聚物(筒称CAA)的合成方法。研究了反应条件对酯化反应得率的影响,以及对共聚物中丙烯酸酯的烷基侧链碳原子数和共聚物单体的不同配比对降凝效果的影响。     

原油降凝剂CAA的合成及降凝效果的研究

本文报导了原油降凝剂丙烯酸烷基酯-丙烯酰胺共聚物(简称CAA)的合成方法。研究了反应条件对酯化反应得率的影响,以及对共聚物中丙烯酸酯的烷基侧链碳原子数和共聚物单体的不同配比对降凝效果的影响。     

共聚物阻垢剂中官能团对CaCO3的阻垢协同作用

以水为溶剂,过硫酸铵为引发剂,丙烯酸、异丙烯膦酸、丙烯酰胺为单体,分别合成了低相对分子质量的丙烯酸/丙烯酰胺(AA/AM)、异丙烯膦酸/丙烯酰胺(IPPA/AM)二元共聚物以及不同配比的丙烯酸/异丙烯膦酸/丙烯酰胺(AA/IPPA/AM)三元共聚物.用红外光谱对产物进行了表征.研究了在相同条件下,含有相同基团的共聚物阻垢剂与复配型阻垢剂以及不同组成的共聚物阻垢剂对CaCO3的阻垢性能.结果表明,同一分子链上的基团间具有较好的阻垢协同效应,且基团组成不同,其阻垢协同效应也不同.     

丙烯酸-丙烯酰胺共聚物的制备及其重金属离子敏感性研究

以部分中和的丙烯酸、丙烯酰胺为单体,过硫酸钾为引发剂,N,N’-亚甲基双丙烯酰胺为交联剂,采用溶液聚合法直接合成出了一系列不同配方的丙烯酸-丙烯酰胺共聚物(PAAAM)。根据其在氯化钠溶液和在氯化铬、硫酸铜溶液中的溶胀度曲线斜率的显著不同,表明此共聚物对重金属离子较为敏感。结果表明,丙烯酰胺配比为40%,丙烯酸中和度为60%,引发剂用量为0.30%,交联剂用量为0.050%(百分比以丙烯酸为基准)条件下合成的PAAAM的重金属离子敏感性较好。     

含磷丙烯酸-AMPS共聚物的合成及阻垢性能研究

以丙烯酸 (AA)、2 -丙烯酰胺 - 2 -甲基丙磺酸 (AMPS)和次亚磷酸钠为单体 ,水为溶剂 ,过硫酸铵为引发剂合成了含磷丙烯酸 - AMPS共聚物阻垢分散剂 (代号 YSS-94)。讨论了单体配比、次亚磷酸钠用量、引发剂用量、反应温度及反应时间对共聚物阻垢性能的影响 ,确定了最佳配比和工艺条件 ,并对产品的阻垢分散性能进行了评价。结果表明 ,该共聚物是一种性能优异的高效水质稳定剂     

AM/DAAM二元共聚物的合成与表征

用一种氧化还原体系的引发剂,采用水溶液聚合法合成了丙烯酰胺-N-(1,1-二甲基-3-氧代丁基)丙烯酰胺(AM/DAAM)二元共聚物。实验中分别考察了原料中单体配比、反应时间、引发剂用量对共聚物的特性粘数的影响;同时采用定量的方法考察了共聚物的溶解性能。结果表明,当DAAM在共聚物中的摩尔百分含量为33.64%时,聚合物的特性粘数比相同条件下合成的聚丙烯酰胺提高9.9倍;当共聚物中DAAM的含量为15%时,共聚物的溶解速率是相同条件下合成的聚丙烯酰胺的4倍。通过对各种组成共聚物在不同盐溶液中的特性粘数的测定,结果显示该共聚物具有良好的耐盐性能。另外,采用红外光谱、核磁共振氢谱对共聚物进行了定性和定量的表征。     

淀粉反相乳液法三元接枝共聚改性研究与表征

以丙烯酰胺(AM)和丙烯酸(AA)为接枝单体,采用反相乳液聚合技术对木薯淀粉进行接枝共聚改性,生成淀粉-丙烯酰胺-丙烯酸三元接枝共聚物(St-g-AM/AA)。考察反应温度和时间、引发剂和单体浓度、单体配比等因素对淀粉三元接枝共聚反应过程的影响规律,并通过红外光谱等表征共聚物结构。实验结果显示:引发剂浓度、单体浓度和单体比、反应温度和时间等因素对三元接枝共聚改性反应影响显著;红外光谱和电镜扫描表征证明接枝共聚反应发生在淀粉颗粒表面,经三元接枝共聚反应淀粉已被AM和AA成功改性。     

Influence of the nature of aggregates on the behaviour of concrete subjected to elevated temperature

An experimental study is carried out on concretes composed of three different types of aggregates: semi crushed silico-calcareous, crushed calcareous and rolled siliceous. For each aggregate type, two water/cement ratios (W/C), 0.6 and 0.3 are studied. Aggregates and concrete specimens were subjected to 300, 600 and 750 °C heating–cooling cycles. We analyse the evolution of thermal, physical and mechanical properties of concrete in terms of behaviour and physical characteristic evolutions of aggregates with temperature. The study of thermal behaviour of aggregates showed the importance of initial moisture state for the flints. The crystallisation and microstructure of quartz play an important role in the thermal stability of siliceous aggregates. The residual mechanical behaviour of concrete varies depending on the aggregate and the influence of aggregates is also dependent on paste composition. This study allowed to better understand the influence of chemical and mineralogical characteristics of aggregates on the thermomechanical behaviour of concrete.     

Effect of the fabrication process on the microstructural evolution of carbon fibers and flexural property on C/SiC composites by the NITE method

Nano-infiltration and transient eutectic phase (NITE) SiC matrix composites are designed for application in aerospace propulsion systems, particularly in fasteners and thrusters. A variety of carbon fibers with different properties have been selected as reinforcements for SiC matrix composites. Carbon fibers are known to be stable at high temperatures; however, the effects of high applied pressure at high temperatures on the fiber microstructure evolution and mechanical properties are not well-known. As a scoping study for fabricating NITE C/SiC composites, the behaviors of various carbon fibers in SiC composites. Pitch-based fibers, namely, GRANOX XN-05 and YS-90A, and a polyacrylonitrile-based fiber, namely, TORAYCA T-300B, were selected for matrix reinforcement. The 3-point bending test results indicated pseudo-ductile behaviors in the cases of YS-90A and T-300B fiber reinforcements. Fracture resistance evaluation based on the single-notch bending test indicated that the YS-90A fiber reinforced composite afforded the highest fracture resistance among the three C/SiC composites. The microstructure evolution on YS-90A and T-300B fibers was limited to near the fiber surface. Therefore, YS-90A and T-300B carbon fibers are potential candidates for reinforcement in NITE C/SiC composites.     

Study of the hydration of CaO powder by gas–solid reaction

Hydration of CaO powders by reaction with water vapor has been studied in isothermal and isobaric conditions. Experimental tests were performed within the temperature range of 70 °C–420 °C and with a water vapor pressure from 5 to 160 hPa by means of a thermogravimetric device. Two powders, exhibiting slight differences in their physical properties, were studied. However, for one of the powders and under some temperature and pressure conditions, the reaction is not complete. The difference of behavior between both CaO powders was interpreted by considering the effect of the morphological properties on the mechanism of growth of Ca(OH)₂.     

Electrophoretically deposited halloysite nanotubes coating as the adsorbent for the removal of methylene blue from aqueous solution

Halloysite nanotubes (HNTs) coatings were prepared by electrophoretic deposition (EPD) from different alcoholic suspensions using polyethyleneimine (PEI) as the dispersant. The results of conductivity, zeta potential, FTIR and thermal analysis showed that PEI is protonated in alcoholic suspensions and then adsorbed on the surface of HNTs enhancing their zeta potential and so colloidal stability. Optimum concentration of PEI decreased with molecular size of alcohol due to the more adsorption of PEI on HNTs. Kinetics of EPD was the fastest from the suspensions with the highest zeta potential. HNTs coatings exhibited high resistance against cracking during their drying due to the self-reinforcement provided by long HNTs and the presence of PEI in their composition which acts as the binder. The coating (6cm²) deposited from ethanolic suspension with 0.5?g/l of PEI (optimum suspension) removed 36% of MB from its aqueous solution (concentration: 5?mg/l and volume: 30?ml) within 2?h.     

Multi-scales modelling for the behaviour of damaged concrete

The aim of this study is to investigate and to simulate damage mechanisms of concrete under fire conditions. A micro-mechanical model has been developed by coupling the effective moduli approach with a finite element model based on the representation of the heterogeneous materials random microstructure. Numerical simulations have been carried out in order to analyze the effective behaviour of confined concrete samples subjected to high temperatures coupled to compressive loads and to localize damage on the microstructure scale. These simulations show that the ‘transient thermal strain’, noticed during experimental tests, is due to the thermal damage of concrete.     

A method based on isothermal calorimetry to quantify the influence of moisture on the hydration rate of young cement pastes

Cement hydration needs water to proceed and if water is lost by drying, the hydration rate will decrease. This can be of importance in cases when concrete surfaces are exposed to drying so that their strength development will be retarded. We describe a method based on isothermal calorimetry to assess how the rate of cement hydration is influenced by removal of water (drying) at different times up to three days after mixing. Thin samples of cement pastes are hydrated in a calorimeter and at different times exposed to one hour drying periods. The resulting decrease in thermal power following the removal of water is quantified as a measure of the reduction in hydration rate. The mass loss is found by weighing the samples before and after a measurement, and the change in water activity of a sample during drying can be found from the slope of the thermal power during the drying period.     

Effect of carbonation on the hydro-mechanical properties of Portland cements

We evaluate experimentally the effect of carbonation on the hydro-mechanical properties of Portland cement. Samples were carbonated at 90 °C and 28 MPa under wet supercritical CO₂. Two types of carbonation features were achieved, either the samples were homogeneously carbonated or they displayed sharp carbonation fronts. Using a tri-axial apparatus, the static elastic moduli and the mechanical strength were measured at in-situ pressure conditions (28 MPa) and showed a degradation of the mechanical properties of the samples where a carbonation front prevailed. Water and gas permeabilities were measured and showed that the samples with a carbonation front exhibit a stress sensitive permeability. P and S elastic wave velocities were measured to evaluate dynamic (ultrasonic range, 1 MHz) elastic moduli. The use of an effective medium theory approach enabled us to characterize the density and distribution of cracks within the samples. This approach outlines that the samples which developed a carbonation front were damaged.     

交联剂的用量对淀粉-壳聚糖-聚乙烯醇-明胶共混膜的性能影响

本文研究了交联剂对淀粉/壳聚糖/聚乙烯醇/明胶共混膜的透光性、透气性、吸水性及保水性和力学性能的影响。结果表明：共混膜的性能与交联剂有较大关系。在交联剂用量在0%~5%的范围内,随着交联剂用量的增加,共混膜的扯断伸长率、吸水性和保水性随之降低,共混膜的拉伸强度、撕裂强度、透水气性和透光性先增加后减小。     

The influence of water removal techniques on the composition and microstructure of hardened cement pastes

The removal of water from hardened cement paste for analysis or to arrest ongoing hydration has been reported to affect the composition of hydrated phases and microstructure. The effect that arresting the hydration of hardened cement paste by replacing the pore water with acetone before drying, and by removing the water by freeze, vacuum and oven drying has on the hardened cement paste has been investigated. Two pastes were studied, a cemented iron hydroxide floc where a high proportion of ordinary Portland cement (OPC) had been replaced by pulverised fuel ash, and a pure hydrated OPC. The results showed that none of the water removal techniques caused any major deterioration in the composition and microstructure of the hardened cement pastes studied, but the pores appeared better preserved after arresting hydration using acetone quenching. Freeze drying appeared to cause more cracking of the microstructure than the other water removal techniques.     

Effect of the variations of clinker composition on the poroelastic properties of hardened class G cement paste

The effect of the variations of clinker composition on the poroelastic properties of class G oil-well cement pastes is studied using a multiscale homogenization model. The model has been calibrated in a previous work based on the results of a laboratory study. Various compositions of class G cements from literature are used in a hydration model to evaluate the volume fractions of the microstructure constituents of hardened cement paste. The poroelastic parameters such as drained bulk modulus, Biot coefficient, and Skempton coefficient are evaluated using the homogenization model. The results show that the variations in chemical composition of class G cements have no important effect on the variations of the poroelastic properties.